Language dominance and reading

Most people have their speech production controlled by the left side of their brain, meaning that they are more likely to develop speech problems after left-sided brain injuries than after right-sided injuries. Up to 30 years ago it was assumed that the cerebral dominance for speech production had no implications for reading, because it was believed that information in the center of the visual field (called the fovea) was projected simultaneously to the left and to the right brain half (bilateral projection). It is becoming clear, however, that this is unlikely to be true (or at least that any overlap is very limited). Letters presented to the left of the fixation point are projected to the right brain half, and letters presented to the right of the fixation location are projected to the left brain half (this is the so-called split-fovea view), meaning that the information of both hemispheres must be integrated before a centrally fixated word can be recognized. This process can be demonstrated empirically by comparing the performance of left dominant participants with that of right dominant participants.

We assessed the brain dominance of 250 lefthanders (who are slightly more likely to have right language dominance), in order to find a reasonably large group of students with reversed language dominance. The performance of this group has been compared to that of typical left dominant participants on a variety of reading tasks and other tasks that have a known lateralization (e.g., symmetry detection, tool use).